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Tang 06 valence bond theory and hybridization

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Hybridization

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Tang 06 valence bond theory and hybridization

  1. 1. VALENCE BOND THEORY & HYBRIDIZATION
  2. 2. VALENCE BOND THEORY Linus Pauling explain how atoms come together and form molecules with the Valence Bond Theory: – A covalent bond forms when two half-filled orbitals overlap to produce a new combined orbital containing two electrons of opposite spin. – This overlapping results in a decrease in the energy of the atoms forming the bond – The shared electron pair is most likely to be found in the space between the two nuclei of the atoms forming the bonds.
  3. 3. Ex. H2 H H 1s1s Overlapping of the 1s orbitals Covalent Bond H-H 1s The newly combined orbital will contain an electron pair with opposite spin just like a filled atomic orbital VALENCE BOND THEORY
  4. 4. In hydrogen fluoride the 1s orbital of the H will overlap with the half-filled 2p orbital of the F forming a covalent bond H F 2p1s + Overlapping of the1s and 2p orbitals + Covalent Bond H-F + VALENCE BOND THEORY Ex. HF
  5. 5. According to the Valence Bond Theory, how many bonds can carbon form? But, how many bonds does carbon really form? VALENCE BOND THEORY 4
  6. 6. Example: Methane (CH4) C HH H H C 2p 2s 1s Lewis dot diagram: Carbon makes 4 bonds Energy level diagram of carbon: How can 3 orbitals form 4 bonds? HYBRIDIZATION
  7. 7. C 2p 2s 1s The orbitals can hybridize with each other to form 4 bonds: 2s and 2p orbitals hybridize Four sp3 hybridized orbitals are formed sp3 sp3 sp3 sp3 Example: Methane (CH4) HYBRIDIZATION
  8. 8. HYBRIDIZATION THEORY • The Hybridization Theory provides a description of the process involving the combination of atomic orbitals to create new bonding orbitals • A hybrid orbital is created by combining at least two different orbitals to produce maximum bonding opportunities • Hybrid orbitals are created through the promotion of electrons One of carbons 2s electrons is promoted to the empty 2p orbital The result produces 4 unpaired electrons for bonding
  9. 9. Recall: Orbital shapes HYBRIDIZATION
  10. 10. Recall: Orbital shapes S P D F HYBRIDIZATION
  11. 11. Hybridized Orbital shapes http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/hybrv18.swf HYBRIDIZATION
  12. 12. How do orbitals hybridize? CC 2p 2s 1s C 2p 2s 1s Hybridized orbitals Hybridized orbitals are wider than non-hybridized orbitals Example: Methane (CH4) HYBRIDIZATION
  13. 13. The 4 bonds fits with the accepted 3D structure of CH4 Example: Methane (CH4) HYBRIDIZATION
  14. 14. What really happens? The nucleus of a hydrogen atom attracts one of the lower-energy valence electrons on carbon. This causes an excitation, moving a 2s electron into a 2p orbital. This, however, increases the attraction of the carbon nucleus on the valence electrons (since the nucleus is slightly less shielded) C 2p 2s 1s H nucleus Example: Methane (CH4) HYBRIDIZATION
  15. 15. What really happens? C 2p 2s 1s sp3 hybridized orbitals 4 hydrogen atoms bond, thus filling every orbital to make a stable product Final product: C H H H H Example: Methane (CH4) HYBRIDIZATION
  16. 16. These are sigma bonds (σ bonds) - a sigma bond is a single, covalent bond - example: sigma bond  Example: Methane (CH4) Overlapping of the1s and 2p orbitals + - results from end-to-end overlap HYBRIDIZATION
  17. 17. Summary Example: Methane (CH4) HYBRIDIZATION
  18. 18. Example: Ethene (C2H4) Structure: sigma bond pi bond -Double bonds are composed of a sigma bond (end-to-end) and a pi (π) bond (side-by-side overlap) -pi are covalent bonds, but are weaker than sigma bonds HYBRIDIZATION
  19. 19. Example: Ethene (C2H4) C 2p 2s 1s The orbitals will hybridize to make 3 sigma bonds + 1 pi bond: One 2s and two 2p orbitals hybridize sp2 sp2 sp2 (not hybridized) HYBRIDIZATION
  20. 20. Example: Ethene (C2H4) How do orbitals hybridize? CC 2p 2s 1s C 2p 2s 1s Hybridized orbitals HYBRIDIZATION
  21. 21. Example: Ethene (C2H4) How do the carbons bond in ethene? C C H H H H Two lobes form one π bond The π bond is symmetrical and above the plane and prevents rotation around the axis between the carbon atoms HYBRIDIZATION
  22. 22. Example: Ethene (C2H4) To draw it more simply… C C H H H H HYBRIDIZATION
  23. 23. Example: Ethene (C2H4) Summary http://www.youtube.com/watch?v=ZsfCPPl13So&feature=related http://www.youtube.com/watch?feature=endscreen&v=C2W-yDPcpl4&NR=1 HYBRIDIZATION
  24. 24. Example: Ethyne (C2H2) π bond σ bond π bond Triple bonds are composed of a sigma bond (end-to-end) and two pi (π) bonds (side-by-side) HYBRIDIZATION
  25. 25. Example: Ethyne (C2H2) C 2p 2s 1s The orbitals will hybridize to make 2 sigma bonds + 2 pi bonds: One 2s and one 2p orbital hybridizes sp sp (non-hybridized p orbitals) HYBRIDIZATION
  26. 26. Example: Ethyne (C2H2) C CH H π bond π bond σ bond HYBRIDIZATION
  27. 27. Example: Ethyne (C2H2) C CH H 1s sp sp sp sp p p p p HYBRIDIZATION
  28. 28. Example: Ethyne (C2H2) Summary HYBRIDIZATION
  29. 29. Example: Benzene (C6H6) http://www.youtube.com/watch?v=-EFEfVDUp6M&feature=related HYBRIDIZATION
  30. 30. Bond Type Hybrids Pure Bond Distribution Single 4 sp3 0 Hybrids make 4 σ bonds Double 3 sp2 1 p π bond is made from pure orbital, σ is made from a hybrid Triple 2 sp 2 p π bonds are made from both pure orbitals, σ is made from a hybrid http://pages.towson.edu/ladon/carbon.html HYBRIDIZATION Summary: Hybridization of Carbon to Make Multiple Bonds
  31. 31. HYBRIDIZATION Hybridization theory explains how boron can make 3 bonds (ex. BCl3) B 2p 2s 1s One 2s and two 2p orbital hybridizes sp2 sp2 (non-hybridized p orbital)sp2
  32. 32. HYBRIDIZATION Hybridization theory explains how boron can make 3 bonds (ex. BCl3)
  33. 33. HYBRIDIZATION Hybridization theory explains how beryllium can make 2 bonds even though its 2s orbital is full (ex. BeCl2) One electron from 2s is promoted to 2p to form two new hybridized orbitals
  34. 34. HYBRIDIZATION Hybridization theory explains how beryllium can make 2 bonds even though its 2s orbital is full (ex. BeCl2)
  35. 35. HYBRIDIZATION Hybridization theory explains how sulfur can make 6 bonds (ex. SF6) 1 electron from 3s is promoted to 3p, and 2 electrons from 3p are promoted to 3d 6 sp3d2 hybridized orbitals are formed
  36. 36. HYBRIDIZATION 1 electron from 3s is promoted to 3p, and 2 electrons from 3p are promoted to 3d
  37. 37. HYBRIDIZATION Hybridization theory explains how sulfur can make 6 bonds (ex. SF6)
  38. 38. HYBRIDIZATION Hybridization theory explains how phosphorus can have a valence of +5 (ex. PCl5) One 3s electron is promoted to 3d, forming 5 hybridized orbitals
  39. 39. HYBRIDIZATION Hybridization theory explains how phosphorus can have a valence of +5 (ex. PCl5) One 3s electron is promoted to 3d, forming 5 hybridized orbitals
  40. 40. HYBRIDIZATION Hybridization theory explains how phosphorus can have a valence of +5 (ex. PCl5)
  41. 41. HYBRIDIZATION Summary Number of groups attached to central atom Hybridization Example Two groups sp BeCl2 Three groups sp2 BCl3 Four groups sp3 CH4 Five groups sp3d PCl5 Six groups sp3d2 SF6
  42. 42. Homework 1. Use the valence bond model or hybridization theory to show the bonding in the following molecules: BeH2, BH3, CCl4, PCl5, SF6 2. Page 238 # 1 – 5, 7, 8, 10 HYBRIDIZATION

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